MACROMOLECULES

A large molecule in which there is a very large number of atoms joined together by

covalent bonds is known as a macromolecule.

A large molecule made up of many repeat units joined together by covalent bonds

Polymer.

A monomer is the starting material for making a polymer.

The process of joining up of many small molecules ( monomers ) to form a long

– chain molecule ( polymer ) is known as Polymerisation.

Addition polymerization is a reaction in which monomers join together to form

a large molecule ( polymer ) as the only product.

Condensation polymerization is a reaction in which monomers join together to form

polymers with the elimination of small molecules.

MACROMOLECULES:

BASIC CONCEPTS

1.1

1. A macromolecule is any long – chain molecule that contains hundreds or thousands

of atoms, joined together by covalent bonds .

2. A macromolecule is formed by linking together many small repeating units

known as monomers.

3. The process of joining together a large number of small molecules ( monomers )

to form a macromolecule is called polymerization . The macromolecule formed

is called a polymer .

COVALENT BONDS

POLYMERISATION

POLYMER

4. Macromolecules are common in living things.

For example, the organic compounds, proteins and starch, found in animals and

plants are examples of natural macromolecules .

5. Synthetic macromolecules, such as plastics, are now manufactured on a large scale.

6. Different macromolecules have different units and different linkages.

ANALYSE:

Describe addition polymerization using the formation of poly (ethane ) form ethane as an example

State some uses of poly ( ethane ) as a typical plastic Deduce the structure of the polymer from a given monomer and vice versa

ADDITION POLYMERISATION:

1. Addition polymerization occurs when monomer units join together without losing

any molecules or atoms.

2. Poly (Ethene)

a) At high pressure and temperature and in the presence of a catalyst , ethene

undergoes addition polymerization to form a long – chain molecule, poly (ethene).

b) Ethene is called the monomer and poly (ethene) is called the polymer.

n POLY ( ETHENE )

ETHENE MONOMERS

1.2

The letter ‘n’ represents a large number. One poly (ethene) molecule contains up

to 30 000 ethene molecules .

c) Uses of poly (ethane):

Poly (ethene ) is widely used as plastic bags, plastic bottles and cling films for

wrapping food.

3. Deducing the structural formula of the polymer from a given monomer:

STEP : 1 Write the structural Formulae of three or four monomers, using

ethene as an example .

H - H H - H H – H

I I I I I I

C = C + C = C + C = C

I I I I I I

H H H H H H

STEP : 2 Open up the carbon – carbon double bonds to form single bonds .

H H H H H H

I I I I I I

- C - C - + - C - C - + - C - C -

I I I I I I

H H H H H H

STEP : 3 Join the monomer molecules together . The structural formula of the polymer

is formed .

H H H H H H

I I I I I I

- C - C - C - C - C - C -

I I I I I I

H H H H H H

Poly ( ethene )

The repeat unit of poly (ethene) is:

CH2 CH2 or H H

I I

C C

I I

H H

The structural formula of poly ( ethene ) can also be written as :

(- CH2 - CH2 -)n or H H

I I

- C - C -

I I

H H n

EXAMPLE1:

a) Write the structural formula of propene.

b) Write the structural formula of the polymer obtained when propene

undergoes addition polymerisation. The structural formula must show

three repeat units.

c) Name the polymer formed.

SOLUTION:

a) H H

I I

CH3 - C = C - H

b) H H H H H H

I I I I I I

- C - C - C - C - C - C -

I I I I I I

CH3 H CH3 H CH3 H

c) Poly (propene)

4. PVC (polyvinyl chloride) plastic is used for making floor coverings, artificial

leather, plastic pipes, raincoats and flooring mats.

H H H H H H

I I I I I I

- C - C - C - C - C - C -

I I I I I I

H Cl H Cl H Cl

PVC plastic

5.Deducing the structural formula of the monomer from a given polymer

STEP :1 Identify the repeat unit in PVC .

H H H H H H

I I I I I I

- C - C - C - C - C - C -

I I I I I I

H Cl H Cl H Cl

repeat unit repeat unit repeat unit

STEP : 2 Write down the structural formula of the repeat unit .

H H

I I

- C - C -

I I

H Cl

STEP : 3 Convert the carbon – carbon single bond into carbon - carbon bond .

H H

I I

C = C

I I

H Cl

Chloroethene

EXAMPLE 2:

Teflon is heat resistant and chemically inert . It has non – stick properties . It is used for coating

non – stick pans . The structural formula of Teflon is shown below .

F F F F F F

I I I I I I

- C - C - C - C - C - C -

I I I I I I

F F F F F F

Write the structural formula of the monomer of Teflon .

SOLUTION:

The repeat unit in Teflon is:

F F

I I

- C - C -

I I

F F

The monomer for Teflon is:

F F

I I

C = C

I I

F F

COMMON ERROR

ACTUAL FACT

Addition polymers can only be made

from a single type of monomer .

Poly ( ethene ) and poly ( propene ) are

made from one type of monomer, i.e. ethene and propene respectively . But addition polymers can also be made from two or more different types of monomers, as long as each monomer contains at least one C = C bond .

ANALYSE:

Describe condensation polymerisation, using nylon (a polyamide ) and Terylene (a polyester ) as examples

State some uses of man – made fibres.

CONDENSATION POLYMERISATION:

1. In condensation polymerisation, small molecules such as water, are eliminated

when monomers join together to form a polymer .

2. For condensation polymerization to occur, each monomer must have two

reactive groups.

The polymer chain is formed by the removal of water molecules .

EXAMPLE :

Dicarboxylic acid (two – COOH groups ) + diamine ( two – NH2 groups )

HOOC – X – COOH + NH2 – Y – NH2 polyamide + H2O

Dicarboxylic acid diamine (e.g. nylon ) water

3.There are two main groups of condensation polymers : polyamides and polyesters .

4. Nylon: A polyamide

a) Nylon is made from two different monomers:

Dicarboxylic acid ( a molecule with two – COOH groups )

Diamine (a molecule with two – NH2 groups )

1.3

b) When the two monomers combine, the polymer, nylon, is formed and water molecules are

eliminated .

O O O O

II II II II

H – O – C – – C – O – H + H - N - - N - H + H - O - C - - C - O - H

Dicarboxylic Acid I I Dicarboxylic Acid

H H

Diamine

Condensation Polymerisation

O O O O

II II II II

– C – – C – N - - N - C - - C - + H2O

I I Water

H H

Parttial Structure Of nylon Polymer

c) The repeat unit of nylon molecule is shown below.

O O

II II

– C – – C – N - - N -

I I

H H

5. Terylene: A polyester

a) Terylene is made from two different monomers:

Dicarboxylic acid

Diol ( an alcohol with two – OH groups )

b) When the two monomers combine, the polymer, Terylene, is formed and water molecules are

eliminated.

Functional Group of Nylon

These Two Groups contain Carbon And Hydrogen atoms and are unreactive.

O H

II I

The – C– N – Group is the

functional group of nylon

and is called the amide

linkage .

Nylon is called a polyamide

because it contains many

amid linkages .

O O O O

II II II II

H – O – C – – C – O – H + H - O - - O - H + H - O - C - - C - O - H

Dicarboxylic Acid Diol Dicarboxylic Acid

Condensation Polymerisation

O O O O

II II II II

– C – – C – O - - O - C - - C - + H2O

Water

Parttial Structure Of Terylene Polymer

c) The repeat unit of Terylene molecule is shown below.

Functional Group Of Terylene

O

II

The – C - O – Group is the

functional group of

Terylene is called the ester

O O

II II

– C – – C – O - - O -

6. Nylon and Terylene are synthetic fibers. They are used for making clothing materials, fishing

lines, parachutes and sleeping bags.

TIPS FOR STUDENTS:

If you are asked to give two uses of a polymer, such as poly (ethene) or Terylene, do not give three uses.

If you write down three uses and one of them is incorrect, your marks will be

deducted for the wrong answer.

These Two Groups contain Carbon And Hydrogen atoms And are unreactive.

COMMON ERROR

ACTUAL FACT

Perspex is used for making plastic lenses. The repeat unit of Perspex is shown below.

H COOCH3

I I

(- C - C-) I I H H

The presence of the ester group, CH3 COO- shows that it is made by condensation polymerisation.

Perspex is not a polyester . It is made by

addition polymerisation. The monomer contains the carbon – carbon double bond as shown below.

H COOCH3

I I

C = C I I H H

DISPOSAL OF NON – BIODEGRADABLE PLASTIC:

1. Non – biodegradable substances are substances that cannot be decomposed by

bacteria in the soil .

2. Currently, most plastic waste is buried in landfill sites. But plastics are non

– biodegradable. They do not decay when thrown away. Thus, they can cause

serious land pollution and waste – disposal problems .

3. Plastics are often disposed of by burning . But this is not a solution as most plastics

1.4

burn to give off toxic fumes. Thus, burning plastics causes air pollution.

TIPS FOR STUDENTS:

Be more specific when answering questions on environment. For example, a disadvantage of using nylon to make fishing nets should not be that

nylon causes pollution or that it is dangerous to sea life . It should be stated that the non – biodegradable property of nylon leads to pollution thus making nylon unsuitable to be used for making fishing nets .

STRUCTURAL QUESTIONS AND ANSWERS

1. Incineration, which means controlled combustion, is a common procedure used

to dispose plastic waste containing poly(ethene).

(a) The formula of poly(ethene) can be taken to be written as (C2H4)n.

(i) Using the formula above, construct a balanced chemical equation to show the polymerisation of ethene.

(ii) Using the formula above, construct a balanced chemical equation or the complete combustion of poly(ethene).

(iii) Draw the structures of ethene and ploy(ethene).

(b) Cracking is one means of recycling waste. Suggest two advantages of cracking over incineration of plastic waste.

ANSWER:

1.a) i) nC2H4 (C2H4)n

ii) (C2H4)n + 3nO2 2nCO2 + 2nH2O

iii)

H H

I I

C = C

I I

H H

ethene

H H

C—C

H H

n

Poly(ethene)

(c) Firstly, cracking converts the used plastics to useful hydrocarbons, such as ethene, which can be used to make other useful chemicals. Secondly, incineration often produces toxic gases, such as carbon monoxide and sulfur dioxide. Cracking leads to less air pollution than incineration.

2. (a) Complete the table below.

Name of polymer Structure of monomer Structure of polymer

H H C C CH3 H n

Poly(1,1-dichloroethene)

(b)What type of polymers are shown above? State the feature present in the monomers of that type of polymers.

ANSWER: 2. (a) Name of the polymer Structure of monomer Structure of polymer

Poly(propene)

H H I I CH3 - C = C - H

Propene

H H C C CH3 H n

Poly (1,1-dichloroethene)

H Cl I I C = C I I H Cl

Dichloroethene

H Cl C C H Cl n

(b) Addition polymers. The C = C double bond present in the monomers of that type of polymers.

3. (a) Write the structural formula of propene.

b) Write the structural formula of the polymer obtained when propene

undergoes addition polymerisation. The structural formula must show

three repeat units.

c) Name the polymer formed.

ANSWER:

a) H H

I I

CH3 - C = C - H

b) H H H H H H

I I I I I I

- C - C - C - C - C - C -

I I I I I I

CH3 H CH3 H CH3 H

c) Poly (propene)

4.)What do you mean by Teflon ?

a.) Draw its structural formula and name its monomer.

b.) Write the use of Teflon.

ANSWER:

Teflon is a polymer formed by addition polymerisation of monomer unit ,

tetrafluroethene. It is heat resistant and chemically inert.

a.) F F F F F F

I I I I I I

- C - C - C - C - C - C -

I I I I I I

F F F F F F

the monomer of Teflon is tetrafluroethene.

F F

I I

C = C

I I

F F

b.) It has non – stick properties. It is used for coating non – stick pans.

5.) a.) Describe condensation polymerization using example.

b.) State some uses of man made fibres.

ANSWER:

a.) Small molecules such as water, are eliminated when monomers join together

to form a polymer in condensation polymerisation.

each monomer must have two reactive groups for condensation polymerization.

The polymer chain is formed by the removal of water molecules.

Dicarboxylic acid (two – COOH groups) + diamine ( two – NH2 groups )

HOOC – X – COOH + NH2 – Y – NH2 polyamide + H2O

Dicarboxylic acid diamine (e.g. nylon) water

Example:

Terylene, it is made from two different monomers:

Dicarboxylic acid (a molecule with two – COOH groups )

Diol ( an alcohol with two – OH groups )

When the two monomers combine, the polymer, Terylene, is formed and water

molecules are eliminated.

O O O O

II II II II

H – O – C – – C – O – H + H - O - - O - H + H - O - C - - C - O - H

Dicarboxylic Acid Diol Dicarboxylic Acid

Condensation Polymerisation

O O O O

II II II II

– C – – C – O - - O - C - - C - + H2O

Water

Parttial Structure Of Terylene Polymer

b. Nylon and Terylene are synthetic fibers.

They are used for making clothing materials,

fishing lines, parachutes and sleeping bags.

SUMMMARY AND KEY POINTS

1.) A macromolecule is a large molecule in which there is a very large number of

atoms joined together by covalent bonds .

2.) A Polymer is a large molecule made up of many repeat units joined together by

covalent bonds .

3.) A monomer is the starting material for making a polymer.

4.) Polymerisation is the process of joining up of many small molecules ( monomers )

to form a long – chain molecule ( polymer ) .

5.) Addition polymerization is a reaction in which monomers join together to form

a large molecule ( polymer ) as the only product.

6.) Condensation polymerization is a reaction in which monomers join together to

form polymers with the elimination of small molecules.

7.) A macromolecule is any long – chain molecule that contains hundreds or thousands

of atoms, joined together by covalent bonds .

8.) A macromolecule is formed by the linking of many small repeating units

known as monomers.

9.) The process of joining together a large number of small molecules ( monomers )

to form a macromolecule is called polymerization . The macromolecule formed

is called a polymer .

10.) Addition polymerization occurs when monomer units join together without losing

any molecules or atoms.

11.) Poly ethene is formed by addition polymerization of ethene at high pressure and

temperature in the presence of a catalyst.

Ethene is called the monomer and poly (ethene) is called the polymer.

12.) PVC (polyvinyl chloride) plastic is a addition polymer which is used for

making floor coverings, artificial leather, plastic pipes, raincoats and

flooring mats.

13.) The polymer is formed when monomers join together by removal of

small molecules such as water is called condensation polymer .

There are two main groups of condensation polymers:

polyamides and polyesters .

14.) Nylon is a polyamide( condensation polymer), made from two different

monomers:

a.)Dicarboxylic acid (a molecule with two – COOH groups)

b.) Diamine (a molecule with two – NH2 groups)

15.) Terylene is a polyester(condensation polymer), is made from two

different monomers:

a.) Dicarboxylic acid

b.) Diol ( an alcohol with two – OH groups )

16.) Nylon and Terylene are synthetic fibers.

They are used for making clothing materials, fishing lines, parachutes

and sleeping bags.

17.) Non – biodegradable substances are substances that cannot be decomposed by

bacteria in the soil .